In recent years, transparent touch panels for realizing an interactive input system have been widely used as one of man-machine interfaces. Transparent touch panels are divided into optical, ultrasonic, capacitance and resistant film types according to position detection method. Out of these, resistant film type transparent touch panels are becoming popular rapidly because they have a simple structure and a high cost/performance ratio.
A resistant film type transparent touch panel is an electronic part which is composed of two films or sheets having a transparent conductive layer on their opposed sides with a predetermined space therebetween. A movable electrode substrate (electrode substrate on a viewer side) is depressed with a pen or finger to be warped and brought into contact and conductive with a fixed electrode substrate (electrode substrate on the opposite side) so as to detect the position of a detection circuit and make a predetermined input. At this point, interference fringes called “Newton rings” may appear in a depressed portion. Even when the electrode substrate is not depressed, “Newton rings” may appear in a narrow space between the movable electrode substrate and the fixed electrode substrate by a warp of the movable electrode substrate. The visibility of a display is reduced by the occurrence of the “Newton rings”. To suppress “Newton rings” which occurs between the two transparent electrode substrates constituting the resistant film type transparent touch panel, JP-A 10-323931 discloses a method of forming a coating layer containing a predetermined amount of a filler having an average primary particle diameter of 1 to 4 μm and a transparent conductive layer on aplastic film. JP-A2002-373056 discloses a method of forming a protrusion coating layer containing silica particles having an average secondary particle diameter of 1.0 to 3.0 μm (coating layer having protrusions) on a plastic film.
In the case of a transparent touch panel comprising a transparent conductive laminate consisting of a plastic film, a coating layer containing particles having an average primary particle diameter or secondary particle diameter in micron order and a transparent conductive layer, both formed on the plastic film, the occurrence of “Newton rings” is reduced. However, when the transparent touch panel is mounted on a high-definition display of nowadays, a resin around the particles contained in the coating layer provides a lens effect, thereby causing the color separation (sparkling) of light from the display and greatly deteriorating the visibility of the display.
As a coating layer for suppressing “Newton rings” other than the above, JP-A 2001-84839 discloses an anti-Newton rings layer which comprises at least two matting agents having different average particle diameters and a binder resin. Although the anti-Newton rings layer formed by this method can suppress sparkling on a high-definition display, particles having different average particle diameters of 1 to 15 μm and 5 to 50 nm are added for matting. When fine particles having an average particle diameter of 5 to 50 nm are added to a binder resin, haze does not occur as the particle diameter is much smaller than the visible light wavelength. From comparison between Examples and Comparative Examples of JP-A 2001-84839, it is presumed that the particles form a secondary agglomerate as the haze value is increased by the addition of the fine particles having an average particle diameter of 5 to 50 nm. It is understood that sparkling is controlled by this rise in haze value, that is, matting. Since the anti-Newton rings layer formed by this method has an extremely large haze value, it deteriorates the visibility of a display.
Further, JP-A 2002-36452 discloses an anti-glare hard coat film comprising a plastic film and a hard coat layer containing a curable resin which is cured by the irradiation of ionizing radiation, silica particles having an average particle diameter of 0.5 to 5 μm and fine particles having an average particle diameter of 1 to 60 μm formed on the plastic film. The purpose of the hard coat layer is to prevent the glare of reflected light from the surface of the hard coat. JP-A 2002-36452 is utterly silent about the method of preventing the sparkling depending on color separation of light from a display and the method of preventing “Newton rings” which occurs between a movable electrode substrate and a fixed electrode substrate, both of which are objects of the present invention.